Many metals can be deposited autocatalytically from baths which include a salt of the metal, a suitable reducing agent, a chelating or complexing agent and a pH-adjusting agent. The surface being plated must either be inherently catalytic for the autocatalytic deposition process, or it must be treated to render it catalytic. Glass and synthetic resins, for example, are not inherently catalytic. Usually, these and other non-catalytic surfaces can be rendered catalytic by, first, treating them with a sensitizing agent such as stannous chloride and then treating them with an activating agent such as palladium chloride. The stannous chloride treatment deposits a film of stannous ions on the surface and the stannous ions reduce some of the palladium salt to palladium. The metal being plated out builds up around palladium nuclei.
Although glass and most resins are readily wetted by solutions of the sensitizing agent and the activating agent, some plastics, such as polytetrafluoroethylene (Teflon), are so hydrophobic in nature that wetting is very non-uniform. This type of surface is difficult to plate autocatalytically. Also, many plastics which are not hydrophobic, still are difficult to plate with an adherent metal coating because they present a highly smooth surface to the metal film being deposited. For this reason, when the article being made requires that the metal coating be strongly adherent, as in making printed circuit boards, for example, the surface being plated must first be roughened to increase its porosity.